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In order to improve the phylogeography of the male-specific genetic traces of Greek and Phoenician colonizations on the Northern coasts of the Mediterranean, we performed a geographically structured sampling of seven subclades of haplogroup J in Turkey, Greece and Italy. We resequenced 4.4 Mb of Y-chromosome in 58 subjects, obtaining 1079 high quality variants. We did not find a preferential coalescence of Turkish samples to ancestral nodes, contradicting the simplistic idea of a dispersal and radiation of Hg J as a whole from the Middle East. Upon calibration with an ancient Hg J chromosome, we confirmed that signs of Holocenic Hg J radiations are subtle and date mainly to the Bronze Age. We pinpointed seven variants which could potentially unveil star clusters of sequences, indicative of local expansions. By directly genotyping these variants in Hg J carriers and complementing with published resequenced chromosomes (893 subjects), we provide strong temporal and distributional evidence for markers of the Greek settlement of Magna Graecia (J2a-L397) and Phoenician migrations (rs760148062). Our work generated a minimal but robust list of evolutionarily stable markers to elucidate the demographic dynamics and spatial domains of male-mediated movements across and around the Mediterranean, in the last 6,000 years.

Huntington's disease is a neurodegenerative disorder caused by an expanded CAG trinucleotide repeat whose length is the major determinant of age at onset but remaining variation appears to be due in part to the effect of genetic modifiers. GRIK2, which encodes GluR6, a mediator of excitatory neurotransmission in the brain, has been suggested in several studies to be a modifier gene based upon a 3′ untranslated region TAA trinucleotide repeat polymorphism. Prior to investing in detailed studies of the functional impact of this polymorphism, we sought to confirm its effect on age at onset in a much larger dataset than in previous investigations. We genotyped the HD CAG repeat and the GRIK2 TAA repeat in DNA samples from 2,911 Huntington's disease subjects with known age at onset, and tested for a potential modifier effect of GRIK2 using a variety of statistical approaches. Unlike previous reports, we detected no evidence of an influence of the GRIK2 TAA repeat polymorphism on age at motor onset. Similarly, the GRIK2 polymorphism did not show significant modifier effect on psychiatric and cognitive age at onset in HD. Comprehensive analytical methods applied to a much larger sample than in previous studies do not support a role for GRIK2 as a genetic modifier of age at onset of clinical symptoms in Huntington's disease.

Succinate semialdehyde dehydrogenase (SSADH; ALDH5A1) deficiency, a rare metabolic disorder that disrupts the normal degradation of GABA, gives rise to a highly heterogeneous neurological phenotype ranging from mild to very severe. The nature of the mutation has so far been reported in patients from six families world wide and eight different mutations were described. Here we report the mutational spectrum in 48 additional unrelated families of different geographic origin. We detected 27 novel mutations at the cDNA level, of which 26 could be attributed to changes at the genomic level. Furthermore, six mutations were detected that did not strongly affect SSADH activity when expressed in HEK 293 cells and are considered nonpathogenic allelic variants. Twenty of the mutations were only found in one family. The spectrum of disease-causing mutations from all patients sequenced thus far consists of 25 point mutations, four small insertions, and five small deletions. Seven of these mutations affect splice junctions, seven are nonsense mutations, and 12 are missense mutations. Although there were no mutational hotspots or prevalent mutations responsible for a significant number of cases, 14 out of 37 (38%) of the missense alleles were present in exon 4 or 5. With one exception, the missense mutations we consider to be causative of SSADH deficiency reduced the SSADH activity to less than 5% of the normal activity in our in vitro expression system. This indicates that residual expression is not likely to be an important factor contributing to the large phenotypic differences observed among different families and even among siblings, suggesting that other modifying factors are of great importance in disease pathology.

Huntington disease (HD) is a neurodegenerative disorder caused by the abnormal expansion of CAG repeats in the HD gene on chromosome 4p16.3. Past studies have shown that the size of expanded CAG repeat is inversely associated with age at onset (AO) of HD. It is not known whether the normal Huntington allele size influences the relation between the expanded repeat and AO of HD. Data collected from two independent cohorts were used to test the hypothesis that the unexpanded CAG repeat interacts with the expanded CAG repeat to influence AO of HD. In the New England Huntington Disease Center Without Walls (NEHD) cohort of 221 HD affected persons and in the HD-MAPS cohort of 533 HD affected persons, we found evidence supporting an interaction between the expanded and unexpanded CAG repeat sizes which influences AO of HD (P = 0.08 and 0.07, respectively). The association was statistically significant when both cohorts were combined (P = 0.012). The estimated heritability of the AO residual was 0.56 after adjustment for normal and expanded repeats and their interaction. An analysis of tertiles of repeats sizes revealed that the effect of the normal allele is seen among persons with large HD repeat sizes (47-83). These findings suggest that an increase in the size of the normal repeat may mitigate the expression of the disease among HD affected persons with large expanded CAG repeats.

We performed a clinical and genetic study of patients affected by cavernous angiomas (CA) of the nervous system. We examined initial signs and symptoms in sporadic and familial cases. We obtained clinical, neuroimaging and genetic data on 15 Italian patients with CA of the nervous system with positive, doubtful or apparently negative family history. Genetic markers surrounding three different gene regions (7q, 3q and 7p) were analysed. In one small family, genetic linkage was consistent with all chromosome loci. In another family with the unusual association of cerebral and spinal CA, linkage with chromosome 7q and, likely, 7p was excluded, while linkage with locus 3q was possible. Our results indicate that Italian families with CA may show genetic heterogeneity. Non-specific and subtle onset symptoms hide the presence of CA within families. Patients with multiple CA may have silent cerebral lesions confirming the low penetrance of clinical signs in spite of radiological ones.

Huntington’s disease (HD) is a neurodegenerative disorder characterized by motor, cognitive, and behavioral disturbances. It is caused by the expansion of the HTT CAG repeat, which is the major determinant of age at onset (AO) of motor symptoms. Aberrant function of N-methyl-D-aspartate receptors and/or overexposure to dopamine has been suggested to cause significant neurotoxicity, contributing to HD pathogenesis. We used genetic association analysis in 1,628 HD patients to evaluate candidate polymorphisms in N-methyl-D-aspartate receptor subtype genes (GRIN2A rs4998386 and rs2650427, and GRIN2B rs1806201) and functional polymorphisms in genes in the dopamine pathway (DAT1 3′ UTR 40-bp variable number tandem repeat (VNTR), DRD4 exon 3 48-bp VNTR, DRD2 rs1800497, and COMT rs4608) as potential modifiers of the disease process. None of the seven polymorphisms tested was found to be associated with significant modification of motor AO, either in a dominant or additive model, after adjusting for ancestry. The results of this candidate-genetic study therefore do not provide strong evidence to support a modulatory role for these variations within glutamatergic and dopaminergic genes in the AO of HD motor manifestations.

Goat mtDNA haplogroup A is a poorly resolved lineage absorbing most of the overall diversity and is found in locations as distant as Eastern Asia and Southern Africa. Its phylogenetic dissection would cast light on an important portion of the spread of goat breeding. The aims of this work were 1) to provide an operational definition of meaningful mtDNA units within haplogroup A, 2) to investigate the mechanisms underlying the maintenance of diversity by considering the modes of selection operated by breeders and 3) to identify the peculiarities of Sardinian mtDNA types. We sequenced the mtDNA D-loop in a large sample of animals (1,591) which represents a non-trivial quota of the entire goat population of Sardinia. We found that Sardinia mirrors a large quota of mtDNA diversity of Western Eurasia in the number of variable sites, their mutational pattern and allele frequency. By using Bayesian analysis, a distance-based tree and a network analysis, we recognized demographically coherent groups of sequences identified by particular subsets of the variable positions. The results showed that this assignment system could be reproduced in other studies, capturing the greatest part of haplotype diversity. We identified haplotype groups overrepresented in Sardinian goats as a result of founder effects. We found that breeders maintain diversity of matrilines most likely through equalization of the reproductive potential. Moreover, the relevant amount of inter-farm mtDNA diversity found does not increase proportionally with distance. Our results illustrate the effects of breeding practices on the composition of maternal gene pool and identify mtDNA types that may be considered in projects aimed at retrieving the maternal component of the oldest breeds of Sardinia.

Two sources of variation in the huntingtin gene, the length of the CCG-rich segment downstream to the (CAG)n stretch undergoing expansion in Huntington disease (HD) and the deletion of 3 bp at codon positions 2642-2645 (delta 2642), were analysed on the normal and HD chromosomes of 80 Italian families affected with HD. No instances of meiotic instability of the CCG-rich segment were detected. A strong linkage disequilibrium was found between the HD mutation and alleles at both polymorphic regions: CCG-rich length alleles different from 176 bp are underrepresented while delta 2642 is overrepresented on HD chromosomes. The presence of such alleles on HD chromosomes does not affect age at onset of the disease. Normal chromosomes displayed a non-random association, shorter (CAG)n segments being preferentially followed by longer CCG-rich segments. Finally, the finding, among normal subjects, of carriers of variants on both chromosomes denotes that variation at either of the two polymorphisms does not impair the function of the huntingtin gene product.

The variability of the Succinic Semialdehyde Dehydrogenase (SSADH, or ALDH5A1) gene affects both pathological and normal phenotypes correlated to cognitive function. We tested the association between the C538T polymorphism of the SSADH gene and preservation of cognitive function in the elderly, and its possible effects on survival. A sample from southern Italy (514 subjects; 18-107 years) was screened for C538T variability. We found that, within the 65-85 years age range, the T/T genotype is overrepresented in subjects with impaired cognitive function (MMSEor = 23) compared to those with conserved cognitive function (MMSE23). Furthermore, we found that the T/T genotype affects survival after 65 years of age. In fact, after this age, the survival function of T/T homozygous subjects is lower than that of the others. Given that the enzymatic activity of the protein encoded by allele T is 82.5% of the activity of the protein encoded by allele C, our results suggest that the efficiency of the SSADH enzyme is important for the preservation of cognitive function and survival in the elderly.

Background Age at onset of Huntington's disease (HD) is correlated with the size of the abnormal CAG repeat expansion in the HD gene; however, several studies have indicated that other genetic factors also contribute to the variability in HD age at onset. To identify modifier genes, we recently reported a whole-genome scan in a sample of 629 affected sibling pairs from 295 pedigrees, in which six genomic regions provided suggestive evidence for quantitative trait loci (QTL), modifying age at onset in HD. Methods In order to test the replication of this finding, eighteen microsatellite markers, three from each of the six genomic regions, were genotyped in 102 newly recruited sibling pairs from 69 pedigrees, and data were analyzed, using a multipoint linkage variance component method, in the follow-up sample and the combined sample of 352 pedigrees with 753 sibling pairs. Results Suggestive evidence for linkage at 6q23-24 in the follow-up sample (LOD = 1.87, p = 0.002) increased to genome-wide significance for linkage in the combined sample (LOD = 4.05, p = 0.00001), while suggestive evidence for linkage was observed at 18q22, in both the follow-up sample (LOD = 0.79, p = 0.03) and the combined sample (LOD = 1.78, p = 0.002). Epistatic analysis indicated that there is no interaction between 6q23-24 and other loci. Conclusion In this replication study, linkage for modifier of age at onset in HD was confirmed at 6q23-24. Evidence for linkage was also found at 18q22. The demonstration of statistically significant linkage to a potential modifier locus opens the path to location cloning of a gene capable of altering HD pathogenesis, which could provide a validated target for therapeutic development in the human patient.

Huntington disease (HD) is caused by the expansion of a CAG repeat within the coding region of a novel gene on 4p16.3. Although the variation in age at onset is partly explained by the size of the expanded repeat, the unexplained variation in age at onset is strongly heritable (h2=0.56), which suggests that other genes modify the age at onset of HD. To identify these modifier loci, we performed a 10-cM density genomewide scan in 629 affected sibling pairs (295 pedigrees and 695 individuals), using ages at onset adjusted for the expanded and normal CAG repeat sizes. Because all those studied were HD affected, estimates of allele sharing identical by descent at and around the HD locus were adjusted by a positionally weighted method to correct for the increased allele sharing at 4p. Suggestive evidence for linkage was found at 4p16 (LOD=1.93), 6p21–23 (LOD=2.29), and 6q24–26 (LOD=2.28), which may be useful for investigation of genes that modify age at onset of HD.

We report the results of a biological and molecular study carried out on 11 Italian families, with a total of 111 individuals in which adult dominant polycystic kidney disease segregates. A restriction fragment length polymorphism analysis was performed. Two families have shown a genetic heterogeneity even if not phenotypically different from the other ones: they resulted unlinked to 16p markers. A prenatal diagnosis has been performed in a family of the linked type.

We analyzed the data on age at onset and CAG size of 319 patients clinically diagnosed with Huntington disease (HD) and 86 presymptomatic subjects recorded by four Italian Centers over the last 14 years. To overcome the problem of different CAG numbers found in each subject, also in the same family, the data were analyzed in terms of deviations from the average exponential relationship between onset and CAG number. The subject's year of birth was also considered to quantify possible sampling biases. Observations between relatives were compared with those of the whole group. The deviations were equal, on average, in subjects who inherited their HD gene from their fathers or mothers. Overall, our data argue in favor of a greater similarity across the same generation than across successive generations. In particular, an excess of parents with later than expected age of onset was observed, paralleled by a CAG-independent anticipation of onset in parent-child transmissions. These results can be interpreted in terms of a shared environment determining similar departures from the average CAG-onset relationship but also of a systematic effect that differentiates the two generations here examined.

Different aspects of expanded polyglutamine tracts and of their pathogenetic role are taken into consideration here. (i) The (CAG) n length of wild-type alleles of the Huntington disease gene was analysed in instability-prone tumour tissue from colon cancer patients to test whether the process leading to the elongation of alleles towards the expansion range involves single-unit stepwise mutations or larger jumps. The analysis showed that length changes of a single unit had a relatively low frequency. (ii) The observation of an expanded spinocerebellar ataxia (SCA)1 allele with an unusual pattern of multiple CAT interruptions showed that cryptic sequence variations are critical not only for sequence length stability but also for the expression of the disease phenotype. (iii) Small expansions of the (CAG) n sequence at the CACNA1A gene have been reported as causing SCA6. The analysis of families with SCA6 and episodic ataxia type 2 showed that these phenotypes are, in fact, expressions of the same disorder caused either by point mutations or by small (CAG) n expansions. A gain of function has been hypothesized for all proteins containing an expanded polyglutamine stretch, including the α 1A subunit of the voltage-gated calcium channel type P/Q coded by the CACNA1A gene. Because point mutations at the same gene with similar phenotypic consequences are highly unlikely to have this effect, an alternative common pathogenetic mechanism for all these mutations, including small expansions, can be hypothesized.

Succinic semialdehyde dehydrogenase (SSADH) deficiency, a rare metabolic disorder of 4-aminobutyric acid degradation, has been identified in approximately 150 patients. Affected individuals accumulate large quantities of 4-hydroxybutyric acid, a compound with a wide range of neuropharmacological activities, in physiological fluids. As a first step in beginning an investigation of the molecular genetics of SSADH deficiency, we have utilized SSADH cDNA and genomic sequences to identify two point mutations in the SSADH genes derived from four patients. These mutations, identified by standard methods of reverse transcription, PCR, dideoxy-chain termination, and cycle sequencing, alter highly conserved sequences at intron/exon boundaries and prevent the RNA-splicing apparatus from properly recognizing the normal splice junction. Each family segregated a mutation in a different splice site, resulting in exon skipping and, in one case, a frameshift and premature termination and, in the other case, an in-frame deletion in the resulting protein. Family members, including parents and siblings of these patients, were shown to be heterozygotes for the splicing abnormality, providing additional evidence for autosomal recessive inheritance. Our results provide the first evidence that 4-hydroxybutyric aciduria, resulting from SSADH deficiency, is the result of genetic defects in the human SSADH gene.

Controversy persists concerning the significance of Huntington disease (HD) alleles in the 36-39 repeat range. Although some clinically affected persons have been documented with repeats in this range, elderly unaffected individuals have also been reported. We examined 10 paternal transmissions of HD alleles of 37-39 repeats in collateral branches of families with de novo HD. All 10 descendants, including many who are elderly, are without symptoms of HD. Forty percent of the transmissions were unstable, although none varied by more than one repeat. The observation that individuals with alleles of 37-39 repeats may survive unaffected beyond common life expectancy supports the presence of reduced penetrance for HD among some persons with repeat sizes which overlap the clinical range. Non-penetrance may be increased in the collateral branches of de novo mutation families when compared to penetrance estimates from patient series. There was no CAA-->CAG mutation for the penultimate glutamine in either a de novo expanded 42 repeat allele or the corresponding non-penetrant 38 repeat allele in a family with fresh mutation to HD.

Four DNA markers on the distal long arm of chromosome 4 have been analyzed for their linkage to facioscapulohumeral muscular dystrophy locus (FSHD) in a series of 16 Italian families. We found that, in two families, the disease is not linked to the 4q35 markers, indicating the presence of genetic heterogeneity among Italian FSHD families. Linkage analysis in the remaining families supports the order cen-D4S171-D4S163-D4S139-D4S810-FSHD-qter, in agreement with the physical map from the literature. EcoRI digestion and hybridization with the distal marker p13E-11 (D4S810)1 detected DNA rearrangements in the affected members of both sporadic and familial cases of FSHD, with family-specific fragments ranging in size between 15 kb and 28 kb. In three sporadic FSHD cases, the appearance of a new “small” fragment not present in either parent was clearly associated with the development of FSHD disease. However, in the familial cases analyzed, we observed two recombinations between all four 4q35 markers and the disease locus in apparently normal subjects, leaving open the possibility of nonpenetrance of the FSHD mutation.

A group of Huntington disease (HD) families of Italian ancestry was analyzed for 11 RFLPs from genetic loci mapped in 4p16 and genetically linked to the HD gene. We found a statistically significant difference of allele distributions in HD vs normal chromosomes for loci D4S10, D4S127, and D4S43. This observation increases the number of loci in linkage disequilibrium with HD. However, the amount of disequilibrium does not allow either a finer localization of the HD gene or a substantial improvement in risk calculations.

The relative frequency of different beta-thalassemia mutations and their association with beta-globin haplotypes were studied in patients from the Nile delta region, Egypt, by means of the polymerase chain reaction, oligonucleotide hybridization and restriction analysis. We found that 8 mutations account for 77% of beta-thalassemia chromosomes in this population, the commonest being IVS-1 nt 110, IVS-1 nt 6 and IVS-1 nt 1. Each mutation was associated with a specific haplotype, with the exception of IVS-1 nt 110, found on 3 different chromosomal backgrounds. Our data show that testing for the 8 detectable mutations makes feasible prenatal diagnosis in 65% of at risk couples and exclusion testing in an additional 25% of cases.

The results of an epidemiological survey on Huntington's disease in the Lazio Region, Central Italy, and of linkage studies in a subset of families are reported. From a total of 99 ascertained families and 491 patients, a prevalence of 25.6 X 10(-6) was obtained, with distributions of age at onset and age at death similar to those described in the literature. No relationship with the sex of the transmitting parent was observed. Analysis of 10 chromosome 4 restriction fragment length polymorphisms in 11 families showed consistent linkage between the genetic loci D4S10, D4S43 and D4S95, and the disease. A recombination rate of 0.08 for D4S10 markers was obtained in this sample. Allelic frequencies of DNA markers in the general population are also reported.

β-thalassemia mutations were characterized in a sample of 70 patients from United Arab Emirates (U.A.E.), resulting in an enlargement of the spectrum of types found in the country. The complete association between the most common IVS I nt 5 (G-C) mutation and a specific haplotype reveals an independent origin of this mutation in U.A.E. © 1995 Wiley-Liss, Inc.

The condition known as the hereditary persistence of fetal hemoglobin (HPFH) is a heterogeneous group of genetically determined anomalies characterized by the presence of increased amounts of Hb F in adult life in the absence of erythropoietic stress (1). Restriction endonuclease analysis has demonstrated that many of these syndromes are due to large deletions in the non-α globin cluster (reviewed in Refs. 1 and 2), whereas in other cases gene sequencing has been necessary to uncover single base substitutions. Point mutations in the promoter regions of the Gγ and Aγ genes have described (3, 4, 5, 6), leading to the suggestion that a single base change can result in persistent gene expression. However, the possibility of simple plymorphisms in linkage disequilibrium cannot be excluded. In particular a CG base change at position -202 of the Gγ gene has been found in 14 cases (six unrelated chromosomes) to be associated with Hb F levels in the rage 13.3-38.1%, most of it being of the Gγ type (6, 7, 8). We re...

The pattern of inheritance of several polymorphic restriction sites associated with the beta-gene cluster, and spanning a region of 52kb, demonstrates that a determinant for hereditary persistence of fetal hemoglobin (HPFH) segregates independently from the non-alpha globin gene cluster, as we postulated several years ago on purely genetical grounds. This finding provides additional evidence for the existence of diffusible factors affecting gamma-chain expression. Moreover, we have identified a "private" HincII polymorphism, in the vicinity of the epsilon gene in the family studied.

We determined by restriction mapping the frequency of the −α3.7 determinant in a random sample of 48 adults in Northern Sardinia. We found a frequency of 0.18±0.04 and demonstrated that only type I crossover as determined by Apa I digestion (Higgs et al. 1984) is present. Moreover, we showed that this haplotype is not associated with an Rsa I polymorphism 5′ to the α2-globin gene. These data support the hypothesis of a unique origin of this deletion in Sardinia.

The relative amounts of HbF, HbA and HbA2 were determined in about 1000 newborns and their parents. In newborns the mean value of HbA2 was 0.27 +/- 0.02% and that of HbF 74.69 +/- 0.25%. The ratio HbA/HbA2 was estimated at different gestational ages and was found to range from 101 at 32 weeks gestation to 76 at 45 weeks, indicating that the relative amount of HbA2 increases with fetal maturation. The correlations between the levels of the different haemoglobins and various indexes of fetal maturation (gestational age, birth weight, crown-heel length and head circumference) are also given.

Analyses of Vital Statistics from various industrialized countries have shown recent reduction of both the rate and sex-ratio of stillbirths. Two alternate explanations are conceivable for the finding: 1) the improvement of environmental conditions has actually reduced the male relative risk, 2) such an improvement has merely postponed late fetal mortality into early periods of extrauterine life. In order to discriminate between these two possibilities, both the secular trends of the sex-ratio of stillbirths and deaths in early infancy were analysed using Italian Vital Statistics. The results can be summarized as follows: 1) the sex-ratio of stillbirths continuously decreased during the examined period, from 1863 to 1979; 2) the sex-ratio of early deaths decreased until about 1920 and thereafter sharply increased. Therefore, Italian data seem to support the hypothesis of a postponement of late fetal deaths into early infant period.

The frequency of deletional alpha-thalassemia in the Egyptian population was estimated at 0.08 by DNA analysis of a newborn random sample. No alpha 0 determinants were found. The most frequent alpha+ determinant was the -alpha 3.7 type I in association with the medium allele at inter-zeta HVR. The -alpha 4.2 and alpha alpha alpha anti 3.7 arrangements were found at very low frequencies.

In the present paper the secular trend of twin concordance for late fetal death rate has been analysed. The results show that, while the correlation remains unchanged in MZ twins, it is greatly reduced in DZ twins. This renders untenable the assumption of comparable secular trends in the intrauterine environment of the two types of twins. An appropriate model is given for the estimation of the environmental (intrauterine) factors in late fetal concordance, under the assumption of a wide range of frequencies for unconditional lethals.

The gene for one form of autosomal dominant spinal cerebellar ataxia (SCA1), is mapped by linkage to chromosome 6p, very close to the microsatellite locus D6S89. Eight large Italian kindreds segregating SCA1, as defined by very close linkage to D6S89, were genotyped with five microsatellite markers linked closely to D6S89, all mapping within a 6 cM interval on 6p. Multipoint linkage analysis and haplotypes from recombinants map SCA1 between two of these markers, D6S274 and D6S259, 5-6 cM apart. A single rare four marker haplotype within this interval shows linkage disequilibrium with the disease locus in southern Italy and is transmitted with SCA1 in five kindreds originating from this area.

The genetic mutation underlying Huntington's disease (HD) has been identified as an expansion and instability of a specific CAG repeat sequence in a gene on chromosome 4. A simple polymerase chain reaction assay has been used for the assessment of the (CAG)n expansion in a 72-year-old woman with typical HD symptoms, but no family history of the disorder. The DNA analysis showed that the patient had an allele with 41 repeat units, in the size range seen in HD chromosomes. Therefore, HD diagnosis is confirmed in this seemingly sporadic case and the disease is newly diagnosed in a large family. The risk of inheriting this unstable expanded allele is discussed. INTRODUCTION--The discovery of an expansion of a trinucleotide (CAG) repeat region in the IT15 gene on the short arm of chromosome 4 has identified the mutational mechanism causing Huntington's disease (HD) and enables the direct diagnosis of affected subjects based on DNA analysis alone. Here a 72-year-old woman with typical HD symptoms, but no family history of the disorder, has been unambiguously diagnosed by using a quick DNA analysis. This is relevant because the disease is newly diagnosed in a large family. MATERIAL AND METHODS--A labelled polymerase chain reaction (PCR) test has been used to amplify the repeat region of the IT15 gene and DNA fragments were analyzed by Polyacrylamide gel electrophoresis. RESULTS--The number the CAG repeats in the proband displayed two alleles of 23 and 41 repeats, respectively. Since normal chromosomes are reported to contain 11-34 repeats, the clinical appearance of HD in the proband is explained by the presence of the repeat expansion. DISCUSSION--The parents of the proposita both died aged over 80 y apparently without neurological signs referable to HD. Hence, this is presumably a sporadic case of the disease. Because of the length of 41 repeats of this HD chromosome, offspring of this proband could inherit the expanded allele with 37 repeats, as expected for the reversal of the trinucleotide expansion. A subject with this intermediate allele could be affected, but would not be affected if the HD IT gene with reduced triplets had recovered its normal function. Thus, in a seemingly sporadic case like the one reported here, despite the PCR analysis, the risk of transmission of HD to her offspring may remain uncertain.

We report the clinical, biochemical and molecular findings on the first documented patient with 4-hydroxybutyric aciduria (4-HBA, McKusick 271980) from Uruguay. The patient displayed a severe picture and turned out to be homozygous for a mutation (c.1226G < A) previously shown to be associated with null enzyme activity.

150 subjects affected with HD and 45 at high risk for the disease were typed for the CAG trinucleotide repeat at the 5' end of IT15. In all of them we find expanded segments showing marked instability upon transmission. Their length distribution matches those previously reported and inversely correlates (-0.686) with age at onset. Two at risk sibs from a large HD pedigree show expanded segments that overlap the normal distribution and can represent reductions from the HD to the normal range. A case of instability on a normal chromosome is also reported. Finally, an analysis of the CAG repeat as a function of three polymorphic DNA markers at D4S127 and D4S95 loci shows no significant difference in the average repeat length on HD chromosomes grouped according to the cosegregating allele of each marker or to the corresponding haplotype. Despite the marked heterogeneity in repeat length among HD families, haplotypes are not associated with different values around which the repeat length fluctuates.

Affected members of 73 families with a variety of autosomal dominant late onset cerebellar ataxias (ADCAs) were investigated for the trinucleotide (CAG) repeat expansion which is found in pedigrees exhibiting linkage to the SCA1 locus OPE chromosome 6. Most of the families were too small for linkage analysis. The mutation was only found in ADCA type I, in 19 out of 38 such kindreds investigated (50%). It was slightly more common in Italian (59%) than British (50%) families, and was also found in Malaysian, Bangladeshi and Jamaican kindreds. Overall, ADCA type I patients with the expansion had a lower incidence of hyporeflexia and facial fasciculation than those without. The trinucleotide expansion was not found in eight families with ADCA and maculopathy or 24 kindreds with a pure type of ADCA, confirming that these syndromes are genetically distinct. It was also not detected in 12 patients with sporadic degenerative ataxias. DNA analysis for the SCAI mutation is useful diagnostically in single patients or small families, and can be used for presymptomatic testing where appropriate.

Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180.

An analysis of genetic fitness was performed in Huntington's Disease (HD) and Spinocerebellar Ataxia 1 (SCA1) families. Two partially overlapping samples were used: clinically defined HD and SCA1 patients from families ascertained in definite geographical areas, and molecularly typed carriers of HD and SCA1 mutations (CAG trinucleotide expansions). In both cases, a control group of normal relatives was used. HD and SCA1 patients born before 1915-20 had more children than normal controls. Carriers of HD and SCA1 mutations, all in the low/medium expansion range (37-49 and 47-54 CAG repeats respectively), had a higher number of children than controls up to more recent times (1935-1950). The reproduction of heterozygotes for large expansions could be analysed only in subjects born after 1950 and provided indirect evidence of a lower than normal number of children. The above results fit a model based on a differential fitness according to the degree of expansion. Such a model predicts that 1) up to relatively recently the frequency of alleles in the low/medium range has been maintained or even increased by the increased fitness of their carriers, as well as by new mutations, and 2) the frequency of large expansions, part of which are lost at each generation, is maintained through further expansions of alleles in the low/medium expansion range. The implications of such a model on linkage disequilibrium and the possible spread of these diseases in future generations are discussed.